1. Field of the Invention
The present invention relates to a forward check valve that controls a flow of a fluid in a forward direction, and to a fuel cell system including the forward check valve.
2. Description of the Related Art
A pressure reducing valve provided for passive driving and used in a small fuel cell is disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093. The pressure reducing valve is formed so that, when the pressure of a fluid becomes a set pressure, the valve automatically opens or closes by making use of a pressure difference.
FIGS. 1A and 1B are each a sectional view of the pressure reducing valve that is disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093. The pressure reducing valve includes a diaphragm 1, a piston 2, a valve seat 3, a valve body 4, and a supporting portion 5. The diaphragm 1 is a movable section. The piston 2 is a transmission mechanism. The valve seat 3, the valve body 4, and the supporting portion 5 constitute a valve portion. The valve body 4 is supported along a periphery thereof by the supporting portion 5. The supporting portion 5 is formed of a resilient bar. Here, each of these members is a plate member. The pressure reducing valve is manufactured by joining each of these members.
Pressure at a top portion of the diaphragm (movable section) 1 is P0, primary pressure at an upstream side of the valve is P1, pressure at a downstream side of the valve is P2, the area of the valve body 4 is S1, and the area of the diaphragm (movable section) 1 is S2. Here, from the equilibrium of the pressures, as shown in FIG. 1B, the condition for opening the valve is (P1−P2)S1<(P0−P2)S2. If P2 is higher than the pressure of this condition, the valve closes, whereas, if P2 is lower than the pressure of this condition, the valve opens. This makes it possible to maintain P2 at a constant value.
For example, a direct methanol fuel cell (DMFC) includes a pump that transports fuel (methanol). In general, although a valve-system pump is provided with a valve non-returning function, the valve-system pump is not provided with a valve forward check function (a function of checking or stopping a flow in a forward direction). If a pump that is not provided with a forward check function is used, when an upstream-side pressure (pressure in a forward direction) is applied to the fuel, the fuel flows even when the pump is not operating.
The temperature of a fuel cartridge that is built in a fuel cell system may become high due to the external environment, as a result of which high-pressure fluid may be discharged. This causes excess fluid to be supplied to a fuel cell, as a result of which the pump may be break. Accordingly, a valve that checks a flow in a forward direction if high-pressure fluid is applied (hereunder referred to as “forward check valve”) is demanded.
In the pressure reducing valve disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093 and shown in FIGS. 1A and 1B, joints of the members contact a fluid. Therefore, if a highly active fluid, such as methanol, is used in the pressure reducing valve, joining strengths may be reduced when the methanol deteriorates interfaces at the joints of the members. In the worst case, the methanol may leak from locations between the members due to peeling of the members.
More specifically, when each member of the pressure reducing valve in Japanese Unexamined Patent Application Publication No. 2008-59093 is bonded with an adhesive, the adhesive is deteriorated by the methanol, as a result of which each member is peeled. This causes the methanol to leak from the locations between the members. Even if each member of the pressure reducing valve in Japanese Unexamined Patent Application Publication No. 2008-59093 is formed of a metallic material, and each member is subjected to diffusion bonding, the methanol enters very small gaps that remain at the interfaces at the joints of the members, as a result of which the interfaces at the joints of the members are corroded.
Therefore, a method of integrally forming each member of the pressure reducing valve in Japanese Unexamined Patent Application Publication No. 2008-59093 out of silicon that is highly resistant to corrosion by methanol may be considered. However, in this method, since it is necessary to use an expensive semiconductor process, manufacturing costs are increased.
Therefore, when an existing forward check valve having the structure of the pressure reducing valve according to Japanese Unexamined Patent Application Publication No. 2008-59093 is manufactured considering manufacturing costs, and a highly active fluid is used in the forward check valve, fluid control cannot be performed with sufficient reliability.